Tentacles can be fun; I've enjoyed many a hentai cartoon involving tentacle rape. But what I really, really enjoy is demons, particularly incubi, and demonically-possessed humans as rapists. I must say, there's just something about a normal person, no apparent supernatural powers, but the fact that he's inhabited by a supernatural
thing giving him all the excuse he needs to rape, torture, and "take revenge" on people he thinks might have wronged him ... that's just hot.